To Verify the Laws of Combination (Series) of Resistances Using a Metre Bridge
Aim
To verify the laws of combination (series) of resistances using a metre bridge.

Apparatus
A metre bridge, a Leclanche cell (battery eliminator), a galvanometer, a resistance box,
a jockey, two resistance wires or two resistance coils known resistances, a set square, sand paper and connecting wires.

Theory where R is the resistance from the resistance box in the left gap and l is the length of the metre
bridge wire from zero end upto balance point. Circuit diagram Procedure
1. Mark the two resistance coils as r1 and r2.
2. To find r1 and r2  proceed same way as in Experiment 1. (If r1 and r2  are not known.)
3. Connect the two coils r1 and r2  in series as shown in figure in the right gap of metre bridge and find the resistance of this combination. Take at least three sets of observations.
4. Record your observations as follows.

Observations
Table for length (1) and unknown resistance (X) Calculations
1. Calculation for r1  only, r2  r2only, r1  and r2 in series.
Same as in Experiment 1.
2. Calculation for verification of laws Experimental value of Rs = ……
Theoretical value of Rs = r1 + r2 = ……
Difference (if any) = ……

Result
Within limits of experimental error, experimental and theoretical values of Rs are same. Hence, law of resistances in series is verified.

Precautions

1. The connections should be neat, clean and tight.
2. Thick copper wires should be used for the connections after removing the insulations near their ends by rubbing with sand paper.
3. Voltmeter and ammeter should be of proper range.
4. A low resistance rheostat should be used.
5. The key should be inserted only while taking observations to avoid heating of resistance (otherwise its resistance will increase).